Apparatus for separating mixtures of solid particles



G. WEBER Dec. 5, 1967 APPARATUS FOR SEPARATING MIXTURES OF SOLID PARTICLES Filed July 16, 1965 United States Patent 3,356,213 APPARATUS FOR SEPARATING MIXTURES OF SOLID PARTICLES Georg Weber, Mannheim-Feudenheim, Germany, assignor to Metallgesellschaft Aktiengesellschaft, Frankfurt am Main, Germany Filed July 16, 1965, Ser. No. 472,638 Claims priority, application Germany, July 16, 1964, M 61,751 7 Claims. (Cl. 209-118) ABSTRACT OF THE DISCLOSURE Pellet containing material coming from a furnace or sintering band is separated into acceptable pellets and rejectable broken pellets and fines by sliding the material down an inclined chute having a series of steps therein. Below the steps is a gap into which the rejects drop. The acceptable pellets jump the gap and are separately collected.

This invention relates to apparatus for separating hot particle size mixtures.

A number of chemical and metallurgical processes car ried out at elevated temperatures in rotary kilns involve the problem of separating the hot solids discharged from the kiln into different particle size fractions and material constituents without previous cooling. This problem arises particularly in the direct reduction of iron ore pellets, if the reduced pellets are to be charged to a succeeding melting furnace at an elevated temperature for improved heat economy.

Various screening devices are known, which are suitable for hot screening. These devices require complicated cooling systems, which extract heat from the material to be separated. Alternatively, the devices must be made from material having a high thermal stability, which involves a low wear resistance and a high capital investment.

It has already been suggested to provide perforated sheet metal bafiies in a rotary kiln near the discharge end thereof for raising the solid mixture from the feeding bed owing to the rotary movement of the kiln so that the fines fall back into the kiln whereas the coarses are fed to a discharge chute. It has also been suggested to incorporate a cylindrical screen, through which the solids to be discharged are passed so that the fines fall also back into the kiln whereas the coarses are discharged.

It is also known to design a part of the kiln wall as a screen. The fines fall through this screen whereas the coarses are discharged at the discharge end of the kiln.

In practice it has been found that these apparatus are subjected to rapid wear, resulting in breakdowns, Owing to the elevated temperatures which are maintained, or they must be made from expensive materials which resist elevated temperatures. These disadvantages are mainly encountered when the process involves a movement of the solids and gas in a counter-current because particularly high temperatures are then obtained at the discharge end of the kiln.

According to a proposal which does not belong to the prior art, these disadvantages are overcome by the use of a frusto-conical screening drum, which is arranged outside the rotary kiln and has a conical surface provided with screening bars, particularly grate bars.

In a known process of separating granular solids by grain size and specific gravity, the feed material is passed in a continuous stream of predetermined thickness across a slope. In this process, a separation is effected because the grains having a lighter specific gravity and the coarser particle size fractions are urged into the upper layer 3,3562 1 3 Patented Dec. 5, 1967 whereas the particles of higher specific gravity and the fines slide into the lower layers.

This process is not suitable for a separation of coarse particle having a relatively high specific gravity from fine particles having a relatively low specific gravity.

It has now been found that the pellet-containing material discharged from furnaces or sintering equipment may be separated by means of a chute having a specific angle in dependence on the different coetlicients of friction of the component particles.

The apparatus according to the invention comprises essentially a separating chute which is inclined from the horizontal at an angle of 20-40, preferably 2535, in a length of -300 centimeters, which chute defines at its lower end a gap having a horizontal width of 40-60 centimeters and is continued by a receiving chute adjoining this gap and having about the same inclination as the separating chute, but has an upper end edge which is vertically spaced about 70100 centimeters below the lower end edge of the separating chute. The feed pipe for the upper chute may incorporate a bafiie, which ensures that the material discharged from the rotary kiln is always supplied to the upper chute in a layer of uniform thickness.

During their downward movement on the separating chute, the various components of the discharged material are accelerated in dependence on their frictional resistance so that the trajectory parabola obtained at the lower end of the separating chute and depending on the speed of the particles, and the dimension of the gap and the height of fall onto the receiving chute cooperate so that the pellets are thrown across the gap onto the receiving chute whereas all other components, such as broken pellets, worn-off material, ashes and surplus coal fall into the gap.

In case of particularly high requirements regarding the purity of the separated products, a plurality of successive separating steps may be carried out. For this purpose the first separating stage is preferably designed so that a product having a desired, high purity is obtained, whereas the second product contains admixtures of the other product. This second product is then separated once more in a second separating stage. The low overall height of the apparatus according to the invention enables an arrangement of two or more separating stages one behind the other and/ or one below the other without difficulty.

In a preferred embodiment of the invention, the upper chute is formed with steps. At each step, a certain preliminary separation of the components is effected so that the overall separation is improved. This is because the material flowing over the steps loosens up so that the larger pieces rise to the top of the material. Thus the fine material is slowed by frictional contact with the chute, while the larger pieces subject to less friction pick up speed and in effect are initially separated from the smaller pieces.

Those surfaces of the chute and of the forwarding means which contact the discharged material consist preferably of refractory material.

The apparatus according to the invention may be an open structure. In those cases in which the discharged material must be subjected to further processing under reducing or neutral conditions, the apparatus may be sealed against an ingress of air.

Special advantages reside in that the overall height and space requirement are very small, mechanically moved parts are not required, those surfaces which are contacted by the discharged material may be made from refractory material and for the above reasons the capital investment and operating costs are low. Besides, the wear is relatively low and repairs can easily be carried out. Another important advantage resides in that the discharged materialcan be subjected to further processing without having been subjected to an enforced cooling. This results in a substantial improvement in heat economy compared to the known processes.

The apparatus according to the invention and its mode of operation will now be explained more in detail and by way of example with reference to the drawing and of examples, which relate to the direct reduction of iron ore in a rotary kiln, followed by a separation of the hot material discharged from the kiln, direct feeding of the pellets into a melting furnace, and cooling the other components in a cooling drum.

EXAMPLE 1 A mixture of reduced iron ore pellets 2, coal, ashes, lime and broken pellets discharged from a rotary kiln 1 was discharged into the end portion 3 of the kiln while being protected against an ingress of atmospheric oxygen, which would tend to oxidize the pellets. By the bafile wall 4, the mixture was spread into a layer of uniform thickness, which is caused to slide down on the stepped separating chute 5. This separating chute 5 was inclined with respect to the horizontal by an angle ot=30. It had a length of 200 centimeters and four steps, each in a height of 6 centimeters. At the lower end of the separating chute 5, the same was formed in its bottom with a gap 6, which had a horizontal width of 600 millimeters. The pellets were thrown across the gap 6 onto the receiving chute 12, which was also inclined at an angle of 30 relative to the horizontal. The upper end edge of chute 12 was vertically spaced 70 centimeters below the lower end edge of the separating chute 5. The hot pure pellets passed to further processing through the opening 11. Coal, ashes, lime and broken pellets fell into the gap 6 and were passed down the chute 9 into the cooler 7. They contained by volume pellets. The top end 10 of the cooler 7 was provided with seals 8 to prevent an ingress of air.

EXAMPLE 2 Chute 9 was designed as a second separating chute and the separated constituents such as ashes, coal, lime and broken pellets were passed into the cooler 7. This product did not contain any pellets.

What is claimed is:

1. Apparatus for separating a mixture of solid particles into large and small particles comprising an inclined separating chute having an upper inlet for receiving the mixture of particles and a lower outlet for discharging large particles, stepped bottom means in said chute for loosening the mixture of particles and initially separating the large and small particles, and gap means in said chute beneath said step means for receiving said small particles and over which the large particles jump.

2. Apparatus as set forth in claim 1, in which said separating chute has an inclination of 20-40 with respect to the horizontal.

3. Apparatus as set forth in claim 2, in which said separating chute has a length of 150-300 centimeters and an inclination of 20-40 with respect to the horizontal.

4. Apparatus as set forth in claim 2, which comprises means for charging said mixture onto said separating chute at a distance of 150-300 centimeters from said lower outlet, measured along the line of inclination of said chute.

5. Apparatus as set forth in claim 4, in which said gap means has a horizontal width of 40 to centimeters.

6. Apparatus as set forth in claim 5, in which said separating chute has an inclination of 2535 with respect to the horizontal.

7. Apparatus as set forth in claim 1, which comprises a refractory lining on those surfaces which are arranged to be contacted by said mixture.

References Cited UNITED STATES PATENTS 413,416 10/1889 Phillips et al. 209-118 579,583 3/1897 Jermyn 209118 1,005,428 10/1911 Hobart 209-418 ALLEN N. KNOWLES, Primary Examiner. 

1. APPARATUS FOR SEPARATING A MIXTURE OF SOLID PARTCLES INTO LARGE AND SMALL PARTICLES COMPRISING AN INCLINED SEPARATING CHUTE HAVING AN UPPER INLET FOR RECEIVING THE MIXTURE OF PARTICLES AND A LOWER OUTLET FOR DISCHARGING LARGE PARTICLES, STEPPED BOTTOM MEANS IN SAID CHUTE FOR LOOSEING THE MIXTURE OF PARTICLES AND INITIALLY SEPARAT- 